There are two main headers used by this library: <boost/regex.hpp>
provides full access to the main template library, while <boost/cregex.hpp>
provides access to the (deprecated) high level class RegEx, and the POSIX
API functions.

There is also a header containing only forward declarations <boost/regex_fwd.hpp>
for use when an interface is dependent upon basic_regex, but otherwise does
not need the full definitions.